A suicide car bomb targeted a US diplomatic vehicle in the volatile city of Peshawar on Monday morning, killing two bystanders and wounding 19, including the passengers.

Remarkably no one inside the car was killed by the huge rush-hour blast, which left a crater in the road and toppled nearby walls. Television footage showed a burned-out four-wheel-drive vehicle at the scene, thought to be the vehicle that was attacked.

Immediately after the blast, the information minister of Khyber Pakhtunkhwa province claimed four people had been killed, including two Americans. But the US state department denied that, saying "two US personnel" and two Pakistani members of staff were injured in the attack, which local police say involved more than 100kg of explosives.

One eyewitness said he saw a severely wounded foreigner being loaded into a vehicle.

"No US consulate personnel were killed, but we are seeking further information about other victims of this heinous act," the statement said.

Over the years the US consulate and its staff in the city, which is close to both the Afghan border and the semi-autonomous tribal areas that are home to a range of militant groups, have been repeatedly attacked.

Last year, a car bomber attempted to target staff from the consulate, which includes diplomats and officials from the United States Agency for International Development, as they drove to work in a convoy of two armoured cars.

The Pakistani Taliban claimed responsibility for the attack, in which a nearby motorcyclist died.

In 2010, militants launched a multi-pronged attack of gunfire, car bombs and rocket-propelled grenades on the heavily fortified consulate itself, killing guards and a Pakistani civilian. In 2008, gunmen launched an unsuccessful attack on the car of the chief US diplomat in the city as her vehicle was leaving her residence.

Also on Monday, trucks carrying supplies to Nato forces in Afghanistan were attacked in the south-west of the country.